2016-03-03 1:44 GMT+09:00 Vlastimil Babka [off-list ref]:

On 02/26/2016 01:58 AM, js1304-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:

quoted

From: Joonsoo Kim <redacted>

Success of CMA allocation largely depends on success of migration
and key factor of it is page reference count. Until now, page reference
is manipulated by direct calling atomic functions so we cannot follow up
who and where manipulate it. Then, it is hard to find actual reason
of CMA allocation failure. CMA allocation should be guaranteed to succeed
so finding offending place is really important.

In this patch, call sites where page reference is manipulated are
converted
to introduced wrapper function. This is preparation step to add tracepoint
to each page reference manipulation function. With this facility, we can
easily find reason of CMA allocation failure. There is no functional
change
in this patch.

In addition, this patch also converts reference read sites. It will help
a second step that renames page._count to something else and prevents
later
attempt to direct access to it (Suggested by Andrew).

Acked-by: Michal Nazarewicz <redacted>
Signed-off-by: Joonsoo Kim <redacted>

Even without Patch 2/2 this is a nice improvement.
Acked-by: Vlastimil Babka <redacted>

Although somebody might be confused by page_ref_count() vs page_count(). Oh
well.

Yes... it was pointed by Kirill before but consistency is not the purpose of
this patchset so I skipped it. There are too many sites (roughly 100) so I'm not
sure this code churn is worth doing now. If someone think it is really
important,
I will handle it after rc2.

Thanks.